The present invention relates to an improvement in plant cutter apparatus of a type where a cutter blade mounted at the distal end of a handling rod is driven by a prime mover or drive source unit.
Generally, weeds growing on footpaths between rice fields etc. Have to be cut several times a year because they tend to be nested by pests. The weed cutting is usually very laborious, and thus various automatic weed cutters have heretofore been proposed and put to practical use, among which shoulder-hung weed cutters are very popular because of their small size and handling ease. In most of the shoulder-hung weed cutters, a driving-force transmission shaft or drive shaft, which is passed through a pipe-shaped handling rod, is rotated via an engine provided at one end of the handling rod so as to rotate a cutter blade provided at the other end of the handling rod. Inmost cases, a human operator hangs the weed cutter on his or her shoulder using a hanging belt, and cuts weeds with the rotating cutter blade by gripping a U-shaped handle provided on an intermediate position of the handling rod to swing the handling rod in front-and-rear and left-and-right directions.
In recent years, there have been strong demands for further improvements in agricultural working environment. In the case of the shoulder-hung weed cutters too, there is an increasing demand for reduction in vibrations that are transmitted from the engine via the handling rod to the U-shaped handle, with a view to lowering the load on the human operator.
Particularly, in the weed cutters where the cutter blade is rotated by the engine via the drive shaft, the vibrations that are transmitted from the engine to the handling rod would present great vibrating amplitude in the rotating direction of the drive shaft. Thus, it is known that minimizing the vibrations in the rotating direction can effectively contribute to reduction of the undesired vibrations transmitted to the handle and hence to the human operator.
Weed cutters arranged to reduce the vibrations transmitted from the engine to the handling rod are known, for example, from Japanese Utility Model Laid-open Publications Nods. 51-64732 and 61-146121. In the weed cutter disclosed in the 51-64732 publication, the engine is mounted, via a clutch housing, at one end of the handling rod through which the drive shaft is passed, and the clutch housing has accommodated therein a clutch operating between the output shaft of the engine and the drive shaft. Further, in the disclosed weed cutter, a connection pipe is secured to the one end of the handling rod and extends toward the engine, and a vibration isolation member is interposed between opposed surfaces of the connection pipe and clutch housing. Thus, the engine is supported by the handling rod via the vibration isolation member in such a manner that vibrations transmitted from the engine to the handling rod can be decreased by means of the vibration isolation member. Namely, the vibration isolation member has two functions: the function of supporting the engine; and the function of attenuating the vibrations transmitted from the engine to the handling rod. In order to enhance or more effectively perform the engine supporting function, the vibration isolation member has to have greater rigidity, which means it is preferable that the vibration isolation member have smaller flexibility. On the other hand, in order to enhance or more effectively perform the vibration isolating function, it is preferable that the vibration isolating member have greater flexibility. Because the vibration isolating function thus tends to be directly influenced by, or correlated with, the engine supporting function, the weed cutter would encounter significant limitations in performing the vibration isolating function.
In the weed cutter disclosed in the 61-146121 publication, the engine is mounted, via a bellows-shaped or tapered vibration isolation member, at one end of the handling rod through which the drive shaft is passed, and the vibration isolation member has accommodated therein a clutch operating between the output shaft of the engine and the drive shaft. Here, the engine is supported by the handling rod via the vibration isolation member in such a manner that vibrations transmitted from the engine to the handling rod can be decreased by means of the vibration isolation member. Because the engine is supported by the handling rod via the vibration isolation member, this disclosed weed cutter can not perform a sufficient vibration isolating function as with the cutter disclosed in the first-mentioned 51-64732 publication.
In view of the foregoing, it is an object of the present invention to provide a plant cutter apparatus which can minimize vibrations transmitted from a drive source unit to a handling rod.
According to the present invention, there is provided an improved plant cutter apparatus of a type which comprises a pipe-shaped handling rod; a drive shaft passed through the pipe-shaped handling rod, a clutch case mounted on one end portion of the handling rod, a drive source unit mounted on the one end portion of the handling rod via the clutch case, and a cutter blade mounted on another end portion of the handling rod for being rotated by rotation, via the drive source unit, of the drive shaft. In the present invention, the clutch case is an integrally-formed, one-piece component part which includes a handling-rod mounting portion coupled to the one end portion of the handling rod, a flexible coupling portion formed to have given flexibility and extending from the handling-rod mounting portion toward the drive source unit, and a drive-source mounting portion extending from the flexible coupling portion and coupled with the drive source unit. The drive-source mounting portion has an axial loosely-fitting hole receiving the one end portion of the handling rod, inserted via the handling-rod mounting portion, in a loosely-fitting engagement such that the one end portion is slid able in an axial direction, and an abutting face or region formed on the way through the loosely-fitting hole for abutting engagement with the end surface of the one end portion.
In the present invention, the clutch case is characterized in that the function of supporting the drive source unit such as an engine and the function of attenuating vibrations transmitted from the drive source unit to the handling rod are performed independently of each other; namely, the clutch case can perform the drive-source supporting function and vibration isolation function separately without an operating correlation between the two functions. Specifically, the drive-source mounting portion can be supported in the axial direction with the end surface of the handling rod abutting against the abutting region of the drive-source mounting portion. The drive source unit is allowed to vibrate about the one end portion of the handling rod supporting the unit. Because the drive source unit is supported by the end surface of the handling rod as noted above, there is no need for the flexible coupling portion to support the drive source unit, so that the flexible coupling portion can fully perform its vibration attenuation function independently of, or without being influenced by, the drive-source supporting function. In the above-described manner, the present invention can significantly reduce the undesired vibrations that are transmitted from the drive source unit to the handling rod while at the same time allowing the rod to reliably support the unit. Further, because the clutch case is an integrally-formed one-piece component, it can decrease the number of parts of the cutter apparatus and thus simplify the construction of the cutter apparatus.
In a specific embodiment, the loosely-fitting hole tapers off toward the abutting region.
In a specific embodiment, the flexible coupling portion has a plurality of circumferential slits each formed in part of a circumference of the flexible coupling portion and communicating with an axial through-hole of the flexible coupling portion, and the plurality of circumferential slits are staggered along the axial direction of the flexible coupling portion. The provision of such circumferential slits allows the flexible coupling portion to have the given flexibility.